There is no centre of the universe! According to the standard theories of cosmology, the universe started with a "Big Bang" about 14 thousand million years ago and has been expanding ever since. Yet there is no centre to the expansion; it is the same everywhere. On a clear, moonless night, one can often see a hazy, luminous band stretching across the sky. The ancients devised many fanciful myths to account for this "milky way." Galileo was the first to look at this haze with a telescope and discover that it was composed of countless dim stars. Today, we realize that this hazy band is our view from the inside of a vast disk that is home to billions of stars, including our own Sun, and vast amounts of interstellar dust. This is our galaxy — the Milky Way.
Earlier in this century, Edwin Hubble's observations led to the discovery that ours is only one of many billions of galaxies that dot the universe with each galaxy home to billions of stars. Some, like the Milky Way, are flat disks with arcing spiral arms and regions of dense interstellar gas, called nebulae, which are active sites of star formation. Yet others are ellipse-shaped agglomerations of mature stars, virtually devoid of interstellar gas or dust.
0 Comments